Fuel pump for a motor vehicle

ABSTRACT

The invention relates to a fuel pump ( 3 ) that is mounted in a fuel tank ( 1 ) of a motor vehicle. Said pump has a preliminary phase ( 6 ) and a principal phase ( 7 ), which are driven by an electromotor ( 5 ). The principal phase ( 7 ) lies directly in front of a flow pipe ( 17 ) to the internal combustion engine. The fuel that is transported by the principal phase ( 7 ) is taken in from a component ( 2, 21 ), into which the fuel of the preliminary phase ( 6 ) has been transported. As the principal phase ( 7 ) is located downstream of the electromotor ( 5 ), an impermissible heating of said electromotor is prevented. The fuel pump ( 3 ) also allows the starting times of the internal combustion engine to be extremely short.

[0001] The invention relates to a fuel pump for a motor vehicle,comprising a preliminary stage and a main stage for delivering the fuelto an internal combustion engine of the motor vehicle, and an electricmotor for driving the preliminary stage and main stage.

[0002] Fuel pumps of this type which are known for petrol or diesel fuelare frequently used in motor vehicles today. The fuel pump as a ruleforms a pre-assemblable, structural unit together with a flange which isto be inserted into an opening in the fuel tank. In this case, theflange bears a connecting branch to which a forward-flow line leading tothe internal combustion engine can be connected, and a connecting branchfor a return-flow line leading back from the internal combustion engine.The fuel fed back from the internal combustion engine is subsequentlyfed to the fuel tank or to a surge chamber. In this connection, thepreliminary stage and the main stage are frequently designed in eachcase as a side-channel pump or peripheral pump, through which the flowpasses axially, and are arranged together at that end of the electricmotor which points towards the bottom region of the surge chamber. Ashaft of the electric motor drives an impeller of the preliminary stageand an impeller of the main stage in each case. The preliminary stageand the main stage are arranged in a common housing together with theelectric motor. The fuel delivered by the main stage flows through theelectric motor.

[0003] One disadvantage of known fuel pumps is that fuel which is notrequired at the internal combustion engine, but is heated up by it, isrecycled into the surge chamber via the return-flow line. During reneweddelivery of this fuel by the fuel pump, the fuel continues to beheated,in particular in the main stage. This may lead to problems as aconsequence of the low heat resistance of the electric motor, inparticular of the carbon-collector system and of the adjacent, electricwiring. For this reason, the temperature of the fuel downstream of themain stage is limited to a permissible value, or the recycled fuel hadto be cooled.

[0004] A further disadvantage resides in the fact that the fueldelivered by the main stage swirls as it flows through the electricmotor. As a result, the fuel has the tendency to form vapor bubbleswhich, together with the fuel, form a foam which negatively affects thereliable supply of the internal combustion engine with fuel.

[0005] Furthermore, when the fuel pump is at a standstill, leakagebetween the main stage and preliminary stage of the fuel pump causes thefuel pump to drain, in which case the motor compartment of the fuel pumpfills with air between the discharge outlet and the main stage.Furthermore, the surge chamber may drain over the same path until levelwith the main-stage bearing point. When the internal combustion engineis restarted, this results, as a consequence of the excessively lowfilling level in the surge chamber, in relatively long starting times orin misfires of the internal combustion engine.

[0006] The invention is based on the problems of designing a fuel pumpof the type mentioned at the beginning in such a manner that theelectric motor of the fuel pump is no longer thermally stressed by thefuel and a rapid and reliable supply of the internal combustion enginewith fuel is ensured.

[0007] According to the invention, these problems are solved in that themain stage of the fuel pump is connected directly to the forward-flowline to the internal combustion engine and is fluidly decoupled from theelectric motor. For this purpose, the suction branch of the main stagehas a connection to a component which is filled with fuel by thepreliminary stage, in particular to a surge chamber or a fuel filter.

[0008] One advantage of the fuel pump according to the invention residesin the fact that the volume of the forward-flow line between the mainstage and the internal combustion engine can be kept very small. Inparticular, the air cushion in previous fuel pumps which forms in theelectric motor between the forward-flow line and the main stage when thefuel pump is at a standstill is avoided. Therefore, when the internalcombustion engine is started with a virtually empty fuel tank, a delayin the delivery of the fuel to the internal combustion engine is keptparticularly small. Furthermore, fuel recycled to the surge chamber orthe fuel tank from the internal combustion engine can be fed at a highertemperature, since, with renewed delivery through the main stage, thefuel which is now hot as a consequence of the heating is no longerguided through the electric motor, but directly into the forward-flowline. An unnecessary heating-up of the electric motor is thereforeprevented. This results in a particularly long life of the electricmotor. Moreover, this design enables swirling by the electric motor ofthe fuel delivered by the main stage to be avoided, with the result thatformation of foam in the forward-flow line is prevented. With the fuelpump according to the invention, a reliable supplying of the internalcombustion engine with fuel is therefore ensured.

[0009] In a particularly advantageous refinement of the invention, themain stage is arranged on that side of the electric motor which liesopposite the preliminary stage. In addition to reducing the length ofthe forward-flow line, this arrangement has the advantage of this fuelpump being very quiet, since the main stage which is primarilyresponsible for the formation of noise has been moved further away fromthe bottom of the fuel tank.

[0010] In a further refinement of the invention, it is advantageous ifthe discharge line of the preliminary stage opens into a surge chamberapproximately level with the main stage or above the suction branch. Itis thereby ensured that, firstly, there is always a sufficient amount offuel available in the surge chamber for the main stage, and that,secondly, the main stage is always filled with fuel, or at leastimmediately sucks in fuel during the starting procedure, and thereforedelivers fuel without delay once the electric motor has started.

[0011] According to another advantageous development of the invention,sucking-in of foamed fuel foam present in the surge chamber can belargely avoided if the main stage has a suction line which is guidedoutside the electric motor into the bottom region of the surge chamber.

[0012] The fuel pump according to the invention can be fitted in aparticularly simple manner if the main stage has, on its side facingaway from the electric motor, a flange having a respective connectingbranch for the suction line and the forward-flow line of said mainstage.

[0013] In another refinement, the discharge line of the preliminarystage is advantageously guided through the electric motor. In additionto the particularly low structural outlay for manufacturing the fuelpump according to the invention, this at the same time enables thebearing points to be lubricated and the carbon-collector system to becooled. However, it is crucial that the fuel fuel heated thereby andtending to give off gas is settled down again by the delivery to acomponent, with the result that bubble-free fuel is sucked in from thiscomponent via the suction branch of the main stage. The inventionpermits numerous embodiments. To further clarify its basic principle,two of these are illustrated in the drawings and are described below. Inthe drawings

[0014]FIG. 1 shows a longitudinal section through a fuel pump,

[0015]FIG. 2 shows a longitudinal section through a different design offuel pump.

[0016] There is arranged in FIG. 1 fuel pump 3 fitted in a surge chamber2 arranged near to a bottom of a fuel tank 1. The fuel pump 3 has ahousing 4 which is manufactured from aluminum or steel and has anelectric motor 5 arranged in it. The electric motor 5 serves for drivinga preliminary stage 6 and a main stage 7. The preliminary stage 6 isarranged near to a bottom of the surge chamber 2, while the main stage 7is situated on the opposite side of the electric motor 5. The surgechamber 2 has, in its bottom region, an opening 8 into which the fuelpump 3 is inserted in a sealing manner. A respective fuel filter 9, 10is situated below the surge chamber 2 and in the upper region thereof.When there is a sufficiently high level of fuel in the fuel tank 1, fuelcan flow through the upper fuel filter 10 into the surge chamber 2. Forclarification purposes, the flows of fuel are indicated in the drawingby arrows. The preliminary stage 6 and the main stage 7 are designed asside-channel pumps and have a respective impeller 12, 13 fastened on ashaft 11 of the electric motor 5.

[0017] The preliminary stage 6 is connected to the fuel filter 9, whichis arranged below the surge chamber 2, via a suction line 14 and isconnected to the surge chamber 2 via a discharge line 15. When thepreliminary stage 6 is being driven by the electric motor 5, thepreliminary stage 6 therefore sucks in fuel from the fuel tank 1 anddelivers it into the surge chamber 2. The discharge line 15 is guidedhere through the electric motor 5 and ends level with the main stage 7.

[0018] The main stage 7 has, on its side facing away from the electricmotor 5, a discharge branch 16 for a forward-flow line 17 and a suctionbranch 18 which is arranged on the circumference of the fuel pump 3 andis intended for a suction line 19. The suction line 19 is guided intothe bottom region of the surge chamber 2 and sucks in the fuel fromthere. The forward-flow line is guided upward within the fuel tank 1.Fuel delivered via the forward-flow line 17 passes to an internalcombustion engine (not illustrated) of the motor vehicle. Fuel which isnot required is conducted via a return flow 20 into the surge chamber 2.This fuel is delivered again to the internal combustion engine by themain stage 7 via the suction line 19 without again flowing through theelectric motor 5.

[0019]FIG. 2 shows a structurally altered design of the fuel pump 3according to the invention. The fuel pump 3 is arranged in a fuel tank1. The discharge line 15 of the preliminary stage 6 is guided throughthe electric motor 5 to a fine fuel filter 21. The main stage 7 is aGerotor pump. The branches 16, 18 for the suction line 19 and theforward-flow line 17 are arranged on that side of the main stage 7 whichfaces away from the electric motor 5. The fuel is sucked in from therethrough the suction branch 18 by the main stage 17 and is passed on tothe internal combustion engine via the forward-flow line 17. Fuel whichis not required is conducted into the fuel tank 1 via a return flow 20.

1. Fuel pump for a motor vehicle, having a preliminary stage deliveringinto a component, preferably a surge chamber or a filter, having a mainstage for delivering fuel via a forward-flow line to an internalcombustion engine and an electric motor for driving the preliminarystage and main stage, characterized in that the main stage (7) sucks infuel from the component (2, 21), and in that the main stage (7) isarranged directly upstream of the forward-flow line (17) to the internalcombustion engine.
 2. Fuel pump according to claim 1, characterized inthat the main stage (7) is arranged on a side of the electric motor (5)which lies opposite the preliminary stage (6).
 3. Fuel pump according toeither of claims 1 and 2, characterized in that a discharge line (15) ofthe preliminary stage (6) opens into the surge chamber (2) in the regionof the main stage (7).
 4. Fuel pump according to claim 3, characterizedin that the discharge line (15) of the preliminary stage (6) opens intothe surge chamber (2) above the suction branch (18) of the main stage(7).
 5. Fuel pump according to at least one of claims 1 to 4,characterized in that the main stage (7) has a suction line (19) whichis guided outside the electric motor (5) into the bottom region of thesurge chamber (2).
 6. Fuel pump according to at least one of claims 1 to5, characterized in that a discharge branch (16) and a suction branch(18) are arranged on the main stage (7), on its side facing away fromthe electric motor (5), preferably on a flange.
 7. Fuel pump accordingto at least one of claims 1 to 6, characterized in that the dischargeline (15) of the preliminary stage (6) is guided through the electricmotor (5).